U.S. patent number 3,920,610 [Application Number 05/463,757] was granted by the patent office on 1975-11-18 for method of making and tailoring prosthetic feet.
Invention is credited to Eugene Wagner.
United States Patent |
3,920,610 |
Wagner |
November 18, 1975 |
Method of making and tailoring prosthetic feet
Abstract
A method of making prosthetic or artificial feet comprising
forming a wooden keel for the ankle portion which has a diminished
heel portion, a flat arch portion, a curved instep portion, a
rounded lower front end portion and a flat top; securing a
reinforcing member comprising a highly resilient synthetic resin
(preferably nylon) strip at its rear end to said flat arch portion
with its front end extending forwardly into a toe portion to be
molded around it to give the toe predetermined flexibility; and
molding a one piece soft resilient foot-forming foam coating under
and around said keel and reinforcing member. The exposed broad
surfaces of said strip may be coated to bond it to said foam
coating. The method of making such artificial feet may provide heel
portions of predetermined variable density and toe portions of
predetermined flexibility to tailor a foot to the characteristics
of an amputee by fashioning the keel with its heel portion properly
diminished for the predetermined heel density, preparing the
reinforcing strip to provide the predetermined toe flexibility by
choice of composition, gauge, length and number of highly resilient
synthetic resin (preferably at least one nylon) strips, securing it
properly to the keel and molding the soft synthetic resin foam
under and around said keel and reinforcing member.
Inventors: |
Wagner; Eugene (Salt Lake City,
UT) |
Family
ID: |
26990239 |
Appl.
No.: |
05/463,757 |
Filed: |
April 24, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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336507 |
Feb 28, 1973 |
3833941 |
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Current U.S.
Class: |
264/46.9;
264/275; 623/55; 264/259; 623/54 |
Current CPC
Class: |
A61F
2/66 (20130101); B29C 44/1271 (20130101); A61F
2002/6657 (20130101) |
Current International
Class: |
B29C
44/02 (20060101); B29C 44/12 (20060101); A61F
2/60 (20060101); A61F 2/66 (20060101); A61F
2/50 (20060101); B29D 027/04 () |
Field of
Search: |
;264/45,271,275
;3/7,6.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Anderson; Philip
Attorney, Agent or Firm: Mortimer; George H.
Parent Case Text
INTRODUCTION
The present invention relates to a method of making prosthetic or
artificial feet of the so-called SACH type, i.e., one having a
solid ankle and cushion heel. This application is a division of my
application Ser. No. 336,507, filed Feb. 28, 1973 now U.S. Pat. No.
3,833,941.
Claims
Having thus described and illustrated the invention, what is
claimed is:
1. The method of making a prosthetic foot comprising forming a keel
having a diminished heel portion, a substantially flat arch
portion, a curved instep portion and a rounded lower front end
portion, fastening to said flat arch portion the rear end of a
reinforcing member comprising a strip of highly resilient synthetic
resin the front end of which extends almost to the end of the toe
to be formed around it, and molding a soft resilient foam coating
comprising toe portion, instep, ankle, heel and arch under and
around said keel and reinforcing member.
2. The method of making a prosthetic foot as set forth in claim 1
in which said reinforcing member is coated prior to the molding
operation with an adherent material that bonds in the molding
operation to the foam coating material in contact therewith.
3. The method of making a prosthetic foot as set forth in claim 1
in which the flexibility of said toe portion as determined by the
herein described toe flexibility test is controlled by the gauge
and structure of the reinforcing member within the limits of 15 mm.
to 50 mm.
4. The method of making a prosthetic foot as set forth in claim 1
in which said reinforcing member comprises a strip of nylon of
predetermined flexibility.
5. The method of making a prosthetic foot as set forth in claim 4
in which said reinforcing member includes a shorter upper
supplemental strip secured to said flat arch portion and to the
longer nylon strip.
6. The method of making a prosthetic foot as set forth in claim 4
in which said strip of nylon is cut from coated oriented
belting.
7. The method of making a prosthetic foot as set forth in claim 6
in which the reinforcing member includes a shorter upper
supplemental strip of coated oriented belting secured to the flat
arch portion and to the longer nylon strip.
8. The method of tailoring a prosthetic foot to the characteristics
of an amputee comprising determining the toe flexibility and heel
density required properly to conform to said characteristics,
fashioning a keel with a substantially flat arch and a diminished
heel to conform to said required heel density, preparing a
reinforcing member of suitable length having at least one nylon
strip to provide said required toe flexibility, securing the rear
end of said member to the flat arch of said keel, and molding a
soft resilient foam covering of polyurethane resin under and around
said keel and member to form a foot comprising a toe portion of
predetermined flexibility, an instep, an ankle, a heel of
predetermined density and an arch.
9. The method as set forth in claim 8 in which said nylon strip is
coated prior to the molding operation with an adherent material
that bonds in the molding operation to the foam covering material
in contact therewith.
10. The method as set forth in claim 8 in which the molding of said
polyurethane is carried out by fashioning said keel with a flat top
portion; firmly mounting said keel upside down in a mold comprising
a flat bottom, an open top and upwardly extending walls conforming
to the finished shape of the visible portions of the foot when it
rests on the sole; preparing a formable polyurethane resin
composition to form the soft resilient foam covering; introducing
the prepared composition through said open top into the space
around said keel and reinforcing strip; placing a cover over said
open top to close the mold and resist the pressure generated;
maintaining the mold closed until the foaming reaction is
completed; and removing the foot from the mold.
Description
BACKGROUND OF THE INVENTION
Various types of artificial or prosthetic feet have been used for
many years. Some of them had been complex devices with many parts
joined together mechanically but in more recent years the most
widely used artificial foot has comprised, (1) an inelastic keel or
core made of wood without any ankle joint; (2) a molded polymer of
rubber or foam plastic completely covering the core except where it
contacts the leg portion of an artificial limb; and (3) either a
flexible steel spring or a band of belting material secured to the
undersurface of the core and extending forwardly of the front end
thereof into the toe section of the molded portion of the foot.
Examples of artificial feet of this type are disclosed in the Nader
U.S. Pat. No. 3,098,239, granted July 23, 1963 and Orange U.S. Pat.
No. 3,484,871, granted Dec. 23, 1969.
Artificial feet made in accordance with the Nader patent, as noted
in the Orange patent, had been found to be too flexible and without
sufficient elasticity. Such feet depend for flexibility and
elasticity on the qualities of the polyurethane foam which develops
fatigue after it has been walked on for a few weeks or months. This
results in loss of balance in the alignment which is given when the
artificial leg was first fitted. The amputee ends up with a toe
section that tends to curl up, to become more and more flexible
with use and, in some cases, the feet break.
Feet made as proposed in the Orange patent are much more expensive
and difficult to manufacture than the Nader feet because of the
numerous parts which have to be assembled, the poor bonds between
the various layers or lamina in the reinforcing member 21-34, the
reliance on polyurethane foam for resilience, and the problems of
separation of the different elements made of polyurethane foam from
one another and from other elements to which adherence is
necessary, all of which tend to make performance
unsatisfactory.
It has also been proposed to provide reinforcement for the toe
portion of an artifical foot by means of a plurality of lamina of
impregnated cords in a sort of triangle, somewhat as illustrated in
Andrews U.S. Pat. No. 616,873, granted Jan. 3, 1899. This type of
artificial foot also operates satisfactorily only as long as the
foam or rubber does not fatigue.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the artifical
feet of the prior art by forming a hardwood core or keel having a
resilient member comprising at least one strip of highly resilient
synthetic resin, preferably nylon, secured thereto and extending
into the toe portion of a cast soft resilient foam covering,
preferably polyurethane, so as to provide the flexibility and
resiliency of the toe portion largely from the resilient member. In
other words, the toe flexibility of feet made in accordance with
this invention do not rely upon the resilience of a molded foam
covering around the core but primarily upon the resilient
member.
This method makes it practicable to provide feet having a wide
range of toe flexibilities so that the amputee can select a foot
which is just right for his weight and other characteristics. The
foot can also be readily provided with a heel density which is
firm, regular or soft. The heel density is thus built-in during
molding so that the foot-forming coating is a one piece molded unit
which has untouched skin even in the heel area. A foot formed in
this manner is a compact unit with no separation of parts and it
can be provided in any desired color since the chemicals are clear
and any color can be reproduced. The finished foot can be sanded
without melting, if necessary, although in general it is not
necessary. It is comparatively light in weight, being between 40 to
80 grams lighter than feet of the prior art and it has consistent
flexibility throughout life with no curling up and breaking of the
toe portion.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a vertical sectional view through a preferred artificial
foot made in accordance with the present invention;
FIG. 2 is a sectional view looking upwardly from a horizontal plane
along the line 2--2 of FIG. 1;
FIG. 3 is a perspective view of a core or keel and attached
resilient strip showing in dotted lines the space to be filled with
polyurethane foam to complete the manufacture of the artificial
foot.
FIG. 4 is a perspective view of a piece of oriented nylon belting
with the near end in section in which the core is a strip of
nylon;
FIG. 5 is a chart of toe flexibilities obtainable in accordance
with the present invention and which can be used to tailor a foot
to the characteristics of an amputee.
DETAILED DESCRIPTION OF THE INVENTION
The artificial or prosthetic foot made by the method of the
invention, as illustrated in FIGS. 1 and 2, is referred to
generally by reference character 1. It comprises a keel 2,
advantageously formed of hardwood, comprising a heel portion 4
which may be diminished in varying degrees as indicated by the
dotted lines for a purpose later to be described, a flat arch
portion 6, a curved instep portion 8 and a rounded front end
portion 9. The keel preferably has a flat top portion 10 to engage
the lower end of the artificial leg with which this foot is
designed to be used, as described in greater detail
hereinafter.
A reinforcing member referred to generally by reference numeral 11
is provided for the purpose of giving controlled flexibility to the
toe portion of the finished foot, as will be described in detail
hereinafter. As illustrated in FIG. 1 the reinforcing member 11
comprises a lower strip 12 and an upper strip 14 fastened at the
rear end to the flat arch portion 6 of the keel 2, e.g. by means of
wood screws 16, so that the front end of said member 11 extends
almost to the end of the toe portionn of the finished foot.
While it is preferred to use a reinforcing member comprising a
plurality of strips, e.g., two, as shown in FIG. 1, the member may
comprise a single nylon strip which would have the length of strip
12, as shown in FIG. 3. In those cases where more than one strip is
used, they should be fastened together, e.g., by an adhesive bond
or by mechanical fastening means such as rivets 18.
Referring now to FIG. 4, the strip or strips used in providing the
reinforcing member 11 comprises a continuous band, strip or ribbon
20 of highly resilient synthetic resin, preferably oriented nylon
which is polyamide resin well known to those skilled in the art,
but other synthetic resins having comparable properties, e.g.,
polyolefins such as polypropylene, may also be used, if desired. By
varying the gauge and composition of the strip or strips, varying
degrees of resilience of the reinforcing member are easily
provided. In general the gauge of the strip is selected within the
range of about 3 to 6 mm. thickness.
Nylon and some other synthetic resins of high resilience do not
form a good bond with resins that form soft resilient foams such as
polyurethane resin foam which is the material preferably used for
molding the foot around the unit comprising the keel and
reinforcing member. Accordingly it is desirable and preferable to
provide a surface covering on one or both sides of the nylon or
like strip, depending upon whether both surfaces are to be exposed
to the polyurethane resin in the molding step. It is not necessary,
for example, to have a surface coating on the contacting surfaces
of nylon strips 12 and 14 when the two strips are secured together
as shown in FIG. 1 but wherever a nylon or like strip is exposed
to, and should bond with, the polyurethane or like foam resin it is
preferable to provide a surface coating on all broad surfaces that
come in contact with the foam resin. This coating is to have the
characteristic of bonding thoroughly to nylon or like plastic and
also bonding thoroughly to polyurethane or like foam resin or other
material used to fashion the foot around the keel and associated
parts. The surface coating 22, for example, may comprise a mixture
of rubber and plastic intimately bonded by welding to a nylon strip
20, or a mixture of rubber latex and carbon black or tar which is
coated on and bonded to the nylon strip, and, if desired, the
coating may also have incorporated therein any of various fabrics
which can be secured by suitable bonding means to the nylon and to
the polyurethane resin when it is molded around the unit comprising
the keel and associated parts. The covering 24 on the other broad
surface may be made of the same materials as the surface covering
22 or from different materials provided they have the same general
characteristics described above.
In order to enable an amputee to fasten the artificial foot to the
bottom of the artifical leg, the keel may be provided with a bolt
hole 36 extending from the flat top surface 10 downwardly through
the keel and with a bolt headhole 38 at the lower end thereof. In
order to provide access to the headhole 38 in the finished foot an
extension 39 of the hole 38 may be provided in the soft resilient
coating as seen in FIG. 1. This is easily accomplished by placing a
plug in 38 during the molding operation which is pulled out when
the foam plastic has cured and the foot is removed from the mold as
described hereinafter. At the bottom of the headhold 38, as viewed
from below, as in FIG. 2, is a shoulder 40 against which the head
of the bolt, a washer or the like, may bear so as to give a good
secure fastening of the foot 1 to the leg (not shown).
After the keel and reinforcing member have been assembled into a
unit as described, the unit may be placed in a mold having the
desired contour for the finished foot and suitably held in place
away from the interior surfaces of the mold a proper distance so as
to provide a covering of soft resilient foam of the desired
thickness at every point under and around the keel and reinforcing
strip. The finished foam covering has a top wall 52 in the plane of
the flat top 10 of the keel 2, as clearly seen in FIG. 1. The
finished foot comprises a heel portion 54, an arch portion 56, a
flexible toe portion 58 and an instep 60. As noted, the instep 60
is curved and follows generally the contour of the curved instep
portion 8 of the keel. The thickness of the foam covering on the
sides of the keel which are not shown in FIG. 1 is comparable to
that shown at the instep portion between the keel 8 and the outside
instep surface 60, as indicated in FIG. 3.
While any desirable method of covering the keel unit with soft
resilient foam may be used, the preferred method comprises
providing a mold comprising a flat bottom wall to which the flat
top 10 of keel 2 can be secured, e.g., by bolt passing through hole
36 which is screwed into a tapped hold in the flat bottom wall.
Upwardly extending walls rising from this bottom wall form an open
top mold cavity conforming to the finished shape of the visible
portions of the foot when it rests on its sole on a flat surface.
An operator fills the cavity between the keel unit and the walls of
the mold cavity through the open top of the mold with a suitably
prepared plastic composition to form the soft resilient foam
covering. After the mold cavity has thus been filled, a cover is
applied to close the open top and its inner surface is contoured to
form the sole of the foot. As those skilled in the art know, the
foaming process develops considerable pressure and requires venting
of air as the plastic swells. To withstand the pressure and keep
the mold cavity tight after venting, the covered mold is preferably
placed in a press that resists the pressure generated in the
foaming reaction which lasts several minutes, e.g., about 15 to 20
minutes, after which the cover may be removed and the foot
withdrawn from the mold.
The heel density, while primarily controlled by the contour of the
heel portion of the keel as later described, may also be controlled
to a desirable degree by the tightness of the packing of the resin
composition in the vicinity of the heel in the open mold. For a
soft heel the packing is light but for a very firm heel the packing
is tight or heavy, with all possible variations between these
extremes.
Polyurethane resin is a particularly desirable material for use in
forming the foam coating around the keel unit in the present
invention but any other resin having similar or equivalent
properties may be substituted, if desired, e.g., rubber, synthetic
resins, and the like.
The SACH type foot requires various degrees of flexibility in the
toes and density in the heel in order to provide different amputees
with a satisfactory fit because of their different height, weight
and other characteristics. The present invention is admirably
adapted to the fitting or tailoring of a prosthetic foot to meet
the varying needs of different amputees.
The heel density can be varied by the simple expedient of changing
the contour of the diminished heel portion 4 as shown in FIG. 1. By
diminishing the heel portion of the keel to the solid line 4, the
heel of the foot will have a soft density because of the larger
amount of yieldable foam resin between the outer surface of the
heel 54 and the surface of the heel portion 4 of keel. On the other
hand if the heel portion 4 of the keel is diminished to the outer
dotted line, the density of the heel of the foot will be more firm.
By diminishing the heel portion of the keel to an intermediate
position, the density of the heel of the foot is predetermined
between those extremes and may be termed regular.
A similar tailoring of the flexibility of the toe is achieved by
one or a combination of variations in the reinforcing member 11.
One way of changing the resiliency and flexibility of member 11 is
by changing the gauge of a single nylon strip, e.g., a 3 mm. strip
would give a soft toe, a 6 mm strip a firmer toe and a 4 mm. strip
an intermediate or regular toe. Generally speaking it is preferable
not to rely solely on the gauge of a single strip for firm toes but
rather to supplement the long strip of the reinforcing member with
an additional strip of somewhat shorter length, as shown in FIG. 1.
By properly selecting the number of strips, the composition and the
gauge thereof it is possible to provide flexibility in the toe
within the entire range of 15-50 mm. as indicated in FIG. 7. The
numerical values of toe flexibility are obtained in a toe
flexibility test on a complete foot made in accordance with the
present invention which is carried out by mounting the foot upside
down with the plane tangent to the sole lying at an angle of
31.degree. to the horizontal and with the toe higher than the heel.
A vertical downward force of 45 kg (about 100 pounds) is then
applied to the toe portion over an area across and for some 5-10
cm. back from the tip of the toe to cause the toe to be deflected
downwardly. A scale calibrated to mm. stands vertically at the side
of the foot with a pointer attached to the tip of the toe at 0 in
unloaded condition. After loading, the position to which the
pointer has been deflected downwardly on the scale is read. It has
been discovered that, under the conditions of this test, firm toes
suitable for use according to this invention give scale readings of
deflection or index numbers that may vary from about 15 to 26 mm.,
regular or medium toes from about 27 to 38 mm. and soft toes from
about 39 to 50 mm. With the same composition gauge and proportions
of the strip or strips in the reinforcing member the toe
flexibility index number varies with shoe size. The following table
gives the range of index numbers a particular example of
construction for a medium toe with shoe size:
TABLE OF TOE FLEXIBILITY ______________________________________
Shoe Size Index Number ______________________________________ 6 28
7 29 8 30 9 31 10 32 11 33 12 34 13 35
______________________________________
Each degree of flexibility from very soft at 50 mm. to very firm at
15 mm. can easily be obtained by proper selection of the number,
composition and gauge of the strip or strips used to form the
reinforcing member.
The present invention is thus a major step forward in the
artificial foot art because it enables the operator in a limb shop
to order feet not only by the density in the heel, either firm,
medium or soft, but also to order feet by the toe flexibility index
numbers at any level within the range of 15-50 mm. This is
important because, for example, a young man with a below the knee
(BK) prosthesis needs a more firm toe than a young man whose leg
has been amputated above the knee (AK) who requires a softer toe.
This can be taken into consideration, for example, by subtracting
1-3 index numbers for a BK amputee and adding 1-3 index numbers for
an AK amputee when ordering a foot in accordance with the
invention. Geriatric, weak or lightweight people also need and
prefer rather soft feet in the toe area while strong walkers,
heavyweight people and the like need more firm toes and higher
density heels. These factors can also be taken into consideration
in ordering feet in accordance with this invention by subtracting
one index number for very active or heavy people and adding one
index number for inactive or light weight people or geriatrics. For
the foot manufacture it requires only routine determination of the
index numbers of feet of different sizes made using varying
compositions, numbers of strips and gauges thereof to obtain
reproduceable specifications for feet having each degree of toe
flexibility from 15-50 mm. so that when an order is received from a
limb shop for a foot of given size having a designated toe
flexibility it is necessary only to refer to the specifications to
determine what reinforcing member needs to be provided to produce
that flexibility in the finished foot. In the present invention,
moreover, the flexibility of the toe is determined almost entirely
by the characteristics of the reinforcing member and not by the
properties of the polyurethane or other foam covering.
There is a readily available commercial source for reinforcing
strips which are admirably adapted for use in the present
invention. This is from the field of transmission belts which are
available in varying widths, gauges and compositions. The main
strip 12, which is used alone or in combination with a strip 14,
should in all cases be nylon or a plastic having equivalent high
resiliency. A transmission belt that is particularly satisfactory
is manufactured by Habasit Company of Switzerland in varying gauges
of oriented nylon from 3 to 6 mm. with coatings tightly adhering to
each broad surface that form good bonds with polyurethane foam
resins. The invention is not limited, however, to Habasit belting
since equivalent nylon or other plastic strips may be used instead,
and, for the preferred process, provided they have coatings on both
broad surfaces thereof which not only adhere tightly to the nylon
core but also form a permanent bond with polyurethane resin under
the molding conditions used in making the feet in accordance with
the present invention. In cases where the desired toe flexibility
can be obtained most satisfactorily by use of a second strip 14
instead of relying for control on gauge alone, the second strip
also is preferably coated nylon of the same width as the first of
main strip but its gauge may be different, if desired. Moreover,
second strips made of a different composition may be used with a
first strip of coated nylon if desired. Thus a foot made by use of
a reinforcing member comprising a coated nylon first strip of 4 mm.
gauge and a shorter strip of rubber impregnated fabric belting of
about the same gauge is commercially acceptable and somewhat less
expensive than a more satisfactory foot made with two nylon
strips.
Although the invention has been described and illustrated in
connection with certain procedures and selection of particular
materials of construction, it will be understood that variations
and modifications may be made without departing from the spirit of
the invention.
* * * * *